This invention relates to the molded case housing for a circuit breaker, and more particularly, to a barrier and venting arrangement for a molded case circuit breaker.
Normally, when a circuit breaker interrupts a fault current, the arc(s) produced during interruption generates hot ionized gases which must be vented from the circuit breaker to avoid rupturing the circuit breaker housing. In a multi-pole circuit breaker, the ionized gas, due to its low dielectric strength, can increase the probability of a fault between the poles of the circuit breaker. Additionally, the ionized gas increases the probability of the occurrene of an arc between the contacts of a circuit breaker and the operating mechanism of a circuit breaker. In addition to having a low dielectric strength, the ionized gas has a substantial amount of energy which is important to disburse.
One way of isolating the current carrying parts of a circuit breaker is illustrated in U.S. Pat. No. 4,242,577. FIGS. 1 and 2 of U.S. Pat. No. 4,242,577 illustrate an insulating barrier for electrically insulating the contacts from the operating mechanism and the toggle means of the circuit breaker. The provision of a barrier within a circuit breaker provides a means for preventing arcing between the operating mechanism and the contacts of a circuit breaker.
While a barrier within a circuit breaker may provide means for inhibiting arcing between the operating mechanism and the contacts of a circuit breaker, it is also important to provide a way of venting hot ionized gases from the circuit breaker. Normally this is done by providing a separate venting channel adapted to vent the ionized gas to the exterior of the circuit breaker housing. A problem with venting hot ionized gas to the exterior of a circuit breaker is keeping the gas away from the line terminals at the exterior. This prevents arcing across the circuit breaker terminals due to the low dielectric strength of the gas.
In addition to providing venting for hot ionized gases, it is useful to provide a means for deionizing and reducing the energy of the ionized gas. An example of deionizing plates is found in U.S. Pat. No. 4,672,157 which illustrates an arc chute fitted with deionizing plates.